Google Hreflang For Mobile First Index: Mobile to Mobile & Desktop to Desktop

John Mueller confirmed today on Twitter that Google's advice around hreflang implementing when it comes to when the mobile first index has been rolled out is to configure it as a "mobile-to-mobile & desktop-to-desktop." Aleyda Solis posted a chart on Twitter to clarify what should be done with the desktop first index versus the mobile first index: You can click on it to enlarge the chart. This makes me wonder even more so that Google really should tell webmasters when their sites migrate over to the mobile first index, to make sure they implement these small things properly when the switch happens. Clearly when a site is on the mobile first index, Google wants the hreflang to be implemented differently here. No?